A headlight device for a vehicle needs to satisfy the conditions of a predetermined light distribution pattern specified by road traffic rules or the like.
As one of the road traffic rules, for example, a predetermined light distribution pattern for an automobile low beam has a horizontally long shape narrow in an up-down direction. To prevent an oncoming vehicle from being dazzled, a boundary (cutoff line) of light on the upper side of the light distribution pattern is required to be sharp. That is, a sharp cutoff line with a dark area above the cutoff line (outside the light distribution pattern) and a bright area below the cutoff line (inside the light distribution pattern) is required.
The illuminance is highest at a region on the lower side of the cutoff line (inside the light distribution pattern). The region of the highest illuminance is referred to as the “high illuminance region.” Here, “region on the lower side of the cutoff line” refers to an upper part of the light distribution pattern, and corresponds to a part for irradiating a distant area, in a headlight device.
A headlight device for a vehicle provides such a complicated light distribution pattern. To provide the complicated light distribution pattern, a light blocking member, such as a shade, is typically used.
Patent Literature 1 discloses a technique in which a shade is disposed at a tip of an optical fiber to form a cutoff line. A sharp cutoff line is formed by disposing the shade at the end of the optical fiber and disposing a light guide lens immediately after the shade in such a manner that a focal position of the lens is located near the shade.